Abscisic acid is one of the plant hormones that determines normal growth and development, i.e. seeds ripening and germination, stomata opening and closure, flowering and stress responses. An appropriate level of endogenous ABA plays a key role in the regulation of most of these processes. Its content in a particular tissue is a balance between the rate of its biosynthesis, oxidative degradation and formation of inactive derivatives (mainly ester). The progress on ABA metabolism was relatively slow in the past. Application of modern molecular biology methods let the most of genes encoding enzymes involved in the regulation of ABA metabolism be identified and contributed to the understanding of its action.